This invention relates to chucks for releasably gripping tools such as drill bits in electric drills.
Many workers in the chuck art have attempted to devise chucks which can be manually tightened on a tool without the need for a separate element such as a key for providing the final tightening action. It is desirable for a chuck to have relatively rapidly moving jaws so that the user does not have to spend a long time rotating the sleeve or other control element which moves the jaws when the chuck must be adjusted to grip tools of different sizes. On the other hand, rapid movement of the jaws typically requires relatively coarse threads in the chuck. Coarse threads decrease mechanical advantage and make it more difficult for the user to tighten the chuck securely on a tool without the provision of some additional tightening element such as a key. While many chucks have keys, they do present some problems For example, they are easily lost, they may be a safety concern (because the key must be removed from the chuck before the tool can be safely used), and they slow down use of the chuck (because they are a separate element which must be fitted into the chuck, operated to tighten the chuck, and then removed from the chuck).
Thus, as noted above, many prior workers have attempted to provide chucks which can be manually tightened on a tool without the need for a key or extremely fine jaw threads which may annoy some users because of the resulting slow motion of the jaws. However, the known prior attempts in this regard have all had significant disadvantages. Some of these prior keyless chucks have required large numbers of additional component parts, which substantially increases manufacturing cost. Some have been more complicated to operate (e.g., because the user must switch from one control element for coarse adjustment of the jaws to another control element for fine adjustment or locking and unlocking of the jaws). Still other prior art keyless chucks have been relatively unreliable (e.g., because the final tightening elements in them are not sufficiently positively controlled during tightening or resetting of the mechanism).
In view of the foregoing, it is an object of this invention to improve and simplify keyless chucks.
It is a more particular object of this invention to provide keyless chucks which do not require large numbers of additional components to provide a tight grip on a tool.
It is another more particular object of this invention to provide keyless chucks which are highly reliable in operation because the operative elements in the chuck are more positively controlled than in many prior keyless chucks.
It is still another more particular object of this invention to provide keyless chucks which can have relatively coarse threads for rapid jaw movement, but which still provide very firm final gripping of a tool.